It is one of the first things people ask when considering a rooflight for their home - do skylights leak? It is a fair question, and the honest answer is: they can, but in most cases they do not have to. When a skylight is made well and fitted correctly, leaks are rare. The problem usually comes down to poor installation, worn seals, or choosing a low-quality product in the first place.
In this guide, we look at why do skylights leak is such a common concern in the UK, what causes it when it does happen, and - more importantly - how to fix a leaking skylight and prevent the issue from occurring at all.
Do Skylights Leak? Here Is the Honest Answer
Modern skylights are far more reliable than older designs. Today's rooflights are built with weatherproof seals, thermally broken frames, and precision-engineered glazing that is specifically designed to keep water out - even in the kind of heavy, persistent rain the UK regularly sees.
That said, do skylights leak in some situations? Yes. But the skylight unit itself is rarely the cause. In most cases, water ingress comes from one of the following:
- A poorly built upstand or kerb around the rooflight
- Flashing that has not been correctly integrated with the roof membrane
- Sealant that has dried out or cracked over time
- A rooflight that was not installed level, causing water to pool
- Condensation being mistaken for a leak
Understanding the difference between these issues is the first step to fixing - or avoiding - the problem altogether.
The Most Common Causes of a Skylight Leaking
1. Poor Installation
This is by far the most common cause of a skylight leaking. If the upstand height is too low, the flashing is not properly bonded to the roof membrane, or the unit is not seated level, water will find its way in. A well-made rooflight can still leak if it has been badly fitted -which is why using an experienced installer matters just as much as buying a quality product.
2. Worn or Cracked Seals
Over time, the sealant around a rooflight can dry out, shrink, or crack, especially after years of exposure to the UK's freeze-thaw weather cycles. This is one of the easier issues to fix. Removing the old sealant and applying a fresh, weather-resistant silicone seal around the frame is usually enough to solve the problem.
3. Damaged or Incorrectly Fitted Flashing
Flashing is the metal or flexible membrane that bridges the gap between the rooflight frame and the surrounding roof surface. If it is corroded, poorly overlapped, or has lifted at the edges, water can track underneath it and into the building. Inspecting the flashing is one of the first things to check if you notice damp patches near a rooflight.
4. A Blocked or Poorly Designed Upstand
On flat roofs, the rooflight sits on a raised upstand that keeps the unit above the roof surface and directs water away. If the upstand is too low or has not been built correctly, standing water can build up and eventually work its way inside. The minimum recommended upstand height for a flat roof rooflight in the UK is 150mm.
5. Condensation - Not a Leak at All
A lot of homeowners contact installers about a leaking skylight when what they are actually seeing is condensation. Condensation forms on the inside of the glass when warm, humid indoor air meets the cold surface of the glazing. It is most common in bathrooms and kitchens, and it tends to appear in the morning when the temperature difference is at its greatest. The fix here is better ventilation or upgrading to a triple-glazed unit with a thermally broken frame - not a new seal or reflashing job.
How to Fix a Leaking Skylight?
The right fix depends on the cause. Here is a straightforward guide to the most common skylight leaking fixes:
|
Problem |
Likely Cause |
Fix |
|
Water around the frame |
Worn or cracked sealant |
Remove old sealant, apply fresh silicone |
|
Water tracking from edge |
Flashing failure |
Rebed or replace flashing, check overlap |
|
Pooling water on flat roof |
Low upstand height |
Raise upstand to minimum 150mm |
|
Condensation on glass |
Poor ventilation or single glazing |
Improve ventilation or upgrade to triple glazing |
|
Water after heavy rain only |
Blocked drainage channel |
Clear debris from around the rooflight frame |
|
Ongoing leak after resealing |
Installation fault |
Have a qualified roofer inspect the full detail |
For minor sealant issues, a confident DIYer can carry out the repair. For anything involving flashing, structural detailing, or a persistent leak with no obvious cause, always get a qualified roofer or rooflight specialist to take a look. Getting it wrong a second time can lead to more costly damage down the line.
How to Prevent Skylights from Leaking
Prevention is always better than a repair call-out. The good news is that avoiding skylight leaks is straightforward when you make the right choices from the start.
Buy a Quality, Certified Product
The single biggest thing you can do to avoid leaks is to buy a rooflight that has been properly tested and certified. At Skylights Roof Lanterns, all of our products are BBA-certified - meaning they have been independently assessed and approved by the British Board of Agrément for weathertightness, durability, and performance in UK conditions. That is not a badge that comes easily, and it gives you genuine reassurance that the product will perform as it should.
Our fixed rooflights are built using toughened glass, weatherproof seals, and precision-engineered frames - and they come with a 10-year manufacturer's guarantee as standard. You can also browse our full range of flat rooflights if you are working on a single-storey extension or flat-roofed build.
Use an Experienced Installer
As we covered earlier, installation is where most leaks begin. Make sure your installer has specific experience fitting the type of rooflight you have purchased. Ask to see previous work, check they will build the upstand to the correct height, and ensure the flashing detail is compatible with your roof membrane.
Inspect Your Rooflight Once a Year
A quick annual check takes no more than ten minutes and can catch small issues before they become expensive ones. Look for any cracking or shrinkage in the sealant, check the flashing is lying flat with no lifted edges, and clear any leaves or debris that might be blocking the drainage path around the frame.
Choose Triple Glazing in Wet or Cold Areas
If your rooflight is going into a bathroom, kitchen, or a room with high humidity, triple glazing is worth the extra cost. It significantly reduces condensation on the inner pane and performs far better in colder months. Many of the products in our skylights collection are available with triple-glazed, self-cleaning glass for exactly this reason.
Why Choosing the Right Product Matters
A cheap rooflight from an unknown supplier might look identical to a BBA-certified unit on paper. But the difference becomes clear the first time a UK winter arrives. Poorly manufactured frames can warp, seals can fail prematurely, and glazing units can develop internal condensation (known as blown units) within just a few years.
Buying from a trusted, specialist supplier - with certified products, a proper guarantee, and a UK-based support team - means that if anything does go wrong, you have someone to call. Browse the full range at Skylights Roof Lanterns or get in touch if you need help choosing the right rooflight for your project.
